This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-334605 filed on Nov. 1, 2000.
1. Field of the Invention
The present invention relates to a pulley unit provided with a one-way clutch.
2. Description of the Related Art
Various accessories installed on a vehicular engine are driven by a belt which receives its rotational energy from the engine""s crankshaft. However, in the case of an alternating current (AC) generator used as an accessory connected in synchronous rotation to the crankshaft of the engine, a decrease in the number of revolutions of the crankshaft is normally experienced, which results in a diminished power generating capacity of the AC generator, during certain modes of the AC generator or its associated driving mechanism.
For avoiding the inconvenience of a reduction of rotational capacity, there is known a method wherein a pulley unit with a one-way clutch is used for the AC generator to improve the generating efficiency during periods of a decreased number of revolutions of the crankshaft.
FIG. 5 is a partial cross-sectional view of a conventional pulley unit incorporating a one-way clutch 120. The conventional pulley unit shown in FIG. 5 comprises a pulley 100 and a shaft 110 which are arranged concentrically and a one-way clutch 120 disposed in an axially intermediate position within a space formed between the pulley 100 and the shaft 110. The one-way clutch 120 comprises an outer ring 122 fixed to the pulley 100, an inner ring 124 fixed to the shaft 110, and a plurality of cylindrical rollers 126 sandwiched in between the outer ring 122 and the inner ring 124. FIG. 3, also a conventional pulley arrangement, shows that between the outer ring 122 and inner ring 124, there are formed wedge-like spaces in multiple positions in the circumferential direction, and the rollers 126 are disposed within those wedge-like spaces, whereby there is formed the one-way clutch 120 which can transfer a rotational driving force in only one direction.
With this pulley unit, a locked state (power transfer state) of the one-way clutch 120 and a free state (power transfer cut-off state) of the one-way clutch 120 are switched from one to the other in accordance with a difference in rotation between a rotor integral with the shaft 110 and the pulley 100. Thus, it is possible to transfer power between the pulley 100 and the rotor and cut off the transfer. Two bearings 130 are provided, respectively, at both axial ends of the one-way clutch 120 to ensure smooth, relative rotation between the pulley 100 and the rotor and lighten the load applied to the clutch from a belt.
In the above conventional pulley unit, when the pulley 100 is rotated by a belt which is secured in the channels of the outer periphery of the pulley 100, a radial load is exerted from the pulley 100 on the rollers 126 of the one-way clutch 120 and also on the bearings 130 disposed on both sides of the rollers. In such a state of use, a clearance allowance between the pulley 100 and the outer ring 122 of the one-way clutch 120 is increased by the radial load exerted from the belt, because the outer ring 122 of the one-way clutch 120 is apt to be distorted radially inwards. Consequently, the wedge-like spaces formed in plural positions in the circumferential direction of the one-way clutch 120 become smaller in radial size and the rollers 126 are displaced which cause the state of the clutch to change. With a decreasing radial size, the wedge angle of each wedge-like space is apt to become small. For example, if the wedge angle becomes smaller than a predetermined lower-limit value, the rollers 126 of the one-way clutch 120 are fixed in the locked state, with no change-over being made to the free state. Thus, the conventional pulley unit has the problem that long-term operational stability can not be achieved due to a deformation of the one-way clutch caused by the radial load from the belt.
Continuing with the conventional pulley unit, FIG. 3 provides a visual example of the outer ring 122 when it is distorted radially inward. Distortion occurs when the wedge angle of each wedge-like space changes from an angle xcex81 in the absence of a distortion of the outer ring 122 to an angle xcex82 in the presence of distortion of the outer ring 122. It follows that the number of revolutions at a change-over between a locked state and a free state will vary depending on the degree of distortion of the outer ring, thereby creating unstable pulley operation.
Moreover, in the above conventional pulley unit, since two bearings 130 are provided at both axial ends of the one-way clutch 120, the number of components used is large and the assembly performance is poor.
The present invention has been accomplished in view of the above-mentioned problems, therefore, it is an object of the present invention to provide a pulley unit which ensures long-term operational stability even with the use of a one-way clutch. It is another object of the present invention to provide a pulley unit with a reduced number of components to thereby attain a reduction in part cost and improvement in assembly performance.
For solving the above-mentioned problems, the pulley unit of the present invention is provided with a one-way clutch between a pulley and a shaft which are concentrically disposed. The one-way clutch comprises an inner ring formed integrally with the pulley, an outer ring formed integrally with the shaft, and rollers accommodated within wedge-like spaces formed between the inner ring and the outer ring. Since the inner ring of the one-way clutch and the pulley are integral with each other, a radial load from the pulley is not transferred to the outer ring and the rollers which are disposed radially outside of the inner ring. This prevents distortion of the outer ring. Consequently, the shape of the wedge-like spaces can be held constant and it is also possible to essentially hold constant the number of revolutions of the pulley, which accommodates transitioning between the locked state and the free state (and vice versa) with movement of the rollers, thus making it possible to ensure long-term operational stability of the pulley. Moreover, since the radial load from the pulley is not imposed on the rollers, it is possible to reduce the roller diameter and it becomes possible to reduce the size of the entire pulley unit.
It is preferable that the pulley and the inner ring be U-shaped and that the one-way clutch be disposed in an annular space inside the pulley. By forming the pulley and the inner ring integrally in a U shape, an interior annular U-shaped space necessary for disposing the one-way clutch is created.
Continuing, it is preferable that two bearings be disposed radially inside of the one-way clutch to receive a load from the pulley. Thus, a load from the pulley can be received directly by the outer ring and the inner ring, which is integral with the pulley, without going through the rollers, etc. in the one-way clutch. In this way the load can be transferred to the shaft by disposing one bearing radially inside of the inner ring and one between the pulley and the outer ring. This positioning in the bearings makes it possible to improve the assembly performance.
It is preferable that clutch cam portions which form the wedge-like spaces have rounded cam surfaces. An inner peripheral surface of the outer ring and/or an outer peripheral surface of the inner ring, opposed to the clutch cam portions, are/is a curved surface and therefore, by forming the clutch cam portions so as to have rounded surfaces, the radial width of each wedge-like space can be changed gently in connection with movement of the rollers in the circumferential direction and it is possible to realize a firmly locked state when the rollers have moved to a particular position.
It is preferable that a retaining piece for holding the rollers not be used. By accommodating the rollers within the wedge-like spaces without the use of a retainer, the number of components used can further be reduced and it becomes possible to attain a further reduction of cost and a further improvement of the assembly performance.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.